1. Field of the Invention
This invention relates generally to a cathode ray tube for an electronic display, on which a pictorial image is produced, and more particularly is directed to a glass front-panel for a cathode ray tube, which is available for a thin-image display apparatus.
2. Description of the Related Art
As a thin image-display apparatus, an apparatus displaying an image by means of a matrix drive system is known, for example, as disclosed in Journal of the Society of Television Engineers, Vol. 40, No. 10.1024 (1986). A glass front-panel for a cathode ray tube available for an image display apparatus comprises an image displaying portion with a flat surface, a side wall portion contiguous to the image displaying portion, and a flange portion crookedly contiguous to the side wall portion, for example, as disclosed in Japanese Laid-open Patent Publication No. 62-153148. The glass front-panel is stuck, with glass frit or the like, to a rear panel made of, for example, a metal plate to form a vacuum vessel.
In such image display apparatus, an electron beam is emitted by an electron gun unit comprising a group of electron-beam-controlling electrodes with a matrix array, and irradiates a phosphor provided on the inner surface of the image displaying portion of the glass front-panel to display an image. To impress the voltage of an electric source to the electron gun unit, a line connecting the electron gun unit to an external terminal is provided. The line passes, for example, through a joint portion, that is, the glass frit lying between the glass front-panel and the rear panel.
However, during the image displaying, a high voltage of several kV or more is generated between the image displaying portion of the glass front-panel and the external terminal having connected to the line passing through the glass frit, which lies between the front panel and the rear panel, so that an electric charge accumulated on the surface of the front glass panel is abruptly released through the bonding layer (portion) and this phenomenon gives rise to the crack on the surface of the bonding layer or the front glass panel.